Coating separator process for producing the same and electrical and electronic parts including the separator

ABSTRACT

This invention provides a separator for electrical and electronic parts with a good electrolyte retention, which is coated with at least one substance selected from ionic substances, hydroxyl group-containing substances and silicon compounds.

TECHNICAL FIELD

This invention relates to a coated separator, process for the productionof the same, and electrical and electronic parts in which the same isused.

BACKGROUND ART

As is symbolized by the recent progress of portable communicationequipments, high-speed processors and the like, it is remarkable thatelectronic equipments have now smaller size and less weight and givehigher performance than before. One of elementary techniques thatcontribute to this tendency is the improvement of electrical andelectronic parts in performance. Batteries are no exception;high-performance parts for batteries are being rapidly developed. Thereis accordingly a growing demand for the development of technology andquality of members, e.g., separator as an interstructure.

For instance, as a variation of alkaline batteries, a cylindricallyshaped one is known. This cylindrical alkaline battery is manufacturedby winding a separator onto a group of grids. In order to increasebattery capacity or to reduce electric resistance, non-woven fabricwhich is used as a separator needs to have a good electrolyte retention.For this purpose, a separator is preferably composed of fibers whichhave as small a diameter as possible. In one of known methods to producesuch non-woven fabric, water stream is sprayed on a fiber web whichcontains divisible fibers which comprise polyolefin resin and aredivisible with water stream, by which to divide the divisible fibers andthereby produce fibers having a small diameter. This method has aproblem that divisible fibers cannot be divided sufficiently, or that alarge amount of energy is required so that fibers may be fully divided.

The objective of this invention is to overcome the above-mentionedproblem, i.e., to provide a separator which has a good electrolyteretention.

DISCLOSURE OF INVENTION

In consideration of the above-mentioned situation, the inventors of thisinvention have made assiduous study with a view to developing aseparator which has a high-level electrolyte retention, and, thus,accomplished this invention.

This invention provides a separator for electrical and electronic partswhich is coated with at least one substance selected from ionicsubstances, hydroxyl group-containing substances and silicon compounds.

This invention also provides a process to manufacture a separator asmentioned above, which is characterized by the following steps: at leastone substance selected from ionic substances, hydroxyl group-containingsubstances and silicon compounds is previously dissolved or dispersed inwater; subsequently, an uncoated separator is soaked in the resultantsolution or dispersion; and then, said separator is dried so thatmoisture may be evaporated.

This invention further provides electrical and electronic parts such asbattery and capacitor wherein a separator of this invention as mentionedabove is used.

In the following, the capacitor of this invention, a process tomanufacture the same, and the use of said capacitor are explained inmore detail.

(Separator)

In this invention, “separator” is defined as a structure to separateconductive members, e.g., electrodes, from each other in electrical andelectronic parts such as battery and capacitor, for the purpose ofpreventing short circuit. Separator is usually employed in the form ofpaper, non-woven fabric, fine porous film or a composite thereof, whichare not restrictive.

As a material for separator, there are often used aramid, polyester,polypropylene, polyethylene, polyphenylene sulfide, fluoroplastic,polyvinyl alcohol, PBO (poly-para-phenylene benzobisoxazole), polyimide,glass, carbon, alumina, natural fiber and natural pulp, since thesematerials are easy to process into paper, non-woven fabric or fineporous film. There is however no particular restriction on materialsinsofar as they have higher resistance than electrode or the like inelectrical and electronic parts.

(Coated Separator)

In this invention, “coated separator” means a separator whose surfacehas, adhered thereon, at least one substance selected from ionicsubstances, hydroxyl group-containing substances and silicon compounds.There is no particular restriction on the amount of said substanceadhered, to the extent that pores of separator are not substantiallyclogged. Generally, however, said amount preferably falls within a rangeof 0.004-20%, in particular 0.01-15%, in dry weight, based on the weightof uncoated separator. Although uniform coating is desirable, unevencoating causes no problem if only separator functions as such.

There is no restriction on coating methods. In a suitable method, atleast one of the above-mentioned substances is dissolved or dispersed inwater; subsequently, a separator is soaked in the resultant solution ordispersion; and then, said separator is dried so that moisture may beevaporated. In another method, an uncoated separator is previouslyintegrated with a part before soaked; subsequently, thus assembled wholepart is soaked in solution or dispersion; and then, said whole part isdried so that moisture may be evaporated. The condition of theabove-mentioned drying is not particularly restricted. Usually, however,drying is preferably conducted at a temperature of 50° C. or higher forone minute or more.

The above-mentioned “part” means an electrical and electronic part suchas battery and capacitor. Such parts include both finished articles andsemi-finished ones so long as they have a space permeative with theabove-mentioned solution.

(Ionic Substances)

“Ionic substances” which are used in this invention mean substanceswherein compound-constituting chemical bond contains ionic bond.Concrete examples include calcium carbonate, calcium chloride, anhydrouscalcium chloride, calcium oxide, sodium chloride, sodium sulfate,anhydrous sodium sulfate, sodium sulfite, copper sulfate, anhydrouscopper sulfate, aluminum sulfate and sodium carboxymethylcellulose,which are not restrictive. Among these, sodium sulfate and anhydroussodium sulfate are preferable.

(Hydroxyl Group-Containing Substances)

“Hydroxyl group-containing substances” which are used in this inventionmean substances which contain a hydroxyl group (—OH) in compound.Concrete examples include alcohols (e.g., ethanol, butanol, etc.),glycols (e.g., ethylene glycol, propylene glycol, etc.) andpolysaccharides (e.g., cellulose, starch, etc.), which are notrestrictive. Among these, polysaccharides are especially preferable.

(Silicon Compounds)

“Silicon compounds” which are used in this invention mean compoundswhich contain silicon. Concrete examples include silica gel, silica sol,silica and zeolite, among which silica is especially preferable,although these are not restrictive.

(Heat Treatment)

In this invention, under circumstances, separator is subjected to heattreatment before and/or after coated, for the purpose of furtherimprovement of electrolyte retention. In particular when a heattreatment is conducted after coating, ionic substance, hydroxylgroup-containing substance or silicon compound or the like is fixed onseparator with the result that electrolyte retention may possibly beremarkably enhanced. There is no strict restriction on temperature ofsaid heat treatment. Generally, however, the temperature is preferablybetween 100° C. and the melting point of separator-constitutingmaterial. Heat treatment may usually be carried out for 1 to 60 minutes.

(Electrolyte Retention)

In this invention, ” electrolyte retention” means the extent to which aseparator sucks up a liquid such as electrolyte within a certain periodof time. Concretely, it is defined as a value which is calculatedaccording to the following formula (1):h²η/γt   (1)

wherein h denotes the height (mm) to which a liquid is sucked up withina period of t seconds; η denotes the viscosity (mP a S) of said liquid;γ denotes the surface tension (mN/m) of said liquid; and t denotessucking time (second).

Generally, the electrolyte retention of the coated separator of thisinvention as shown by the above-mentioned formula (1) is preferably 0.7μm or more, especially 1 μm or more.

The separator of this invention which has been coated in theafore-mentioned manner has a good electrolyte retention owing tocoating, and is quite suitable as a separator panel between conductivemembers of electrical and electronic parts.

EXAMPLES

In the following, this invention is explained in more detail by Exampleand Comparative Example.

(Method for Measurement)

(1) Measurement of the Basis Weight and the Thickness of Sheet:

Measured according to JIS C2111.

(2) Measurement of Sucking Height:

The height to which n-butanol was sucked up within a period of 30seconds was measured.

At 20° C., n-butanol had a viscosity of 7 (mP a S) and a surface tensionof 24.6 (mN/m).

Example 1

Fibrid of polymetaphenylene isophthalamide was manufactured with a wettype precipitator as mentioned in Japanese Patent Publication No. Sho 52(1977)-151624. Thus obtained fibrid was treated with a refiner so thatdrainage rate (Canadian standard freeness) might become 20 ml.

Aramid fiber (Conex®, manufactured by Teijin Limited) was cut to alength of 5 mm to serve as paper stock (aramid flock). This flock had afineness of 0.8 denier.

Thus prepared stock was mixed with each other in water, and was thenmade into sheet with TAPPI standard sheet machine (surface area: 625cm²).

Said sheet was subjected to calendering process with a calenderingmachine at a roll temperature of 330° C., a roll linear pressure of 100kgf/cm, and at a rate of 2 m/min.

Thus calender-processed sheet was soaked in a 0.25% aqueous solution ofsodium sulfate for one minute, and was then dried in a hot air oven at150° C. for 30 minutes.

Thus obtained sheet material was measured for main properties andbutanol-sucking height. Results are shown in Table 1.

Comparative Example 1

The steps of Example 1 were repeated up to calendering process, and,then, thus processed sheet was soaked in high purity water for oneminute, and was then dried in a hot air oven at 150° C. for 30 minutes.

Thus obtained sheet material was measured for main properties andbutanol-sucking height. Results are shown in Table 1. TABLE 1 ExampleComparative Properties Unit 1 Example 1 Composition of material Aramidfibrid Weight % 10 10 Aramid flock 90 90 Basis weight g/m² 10 10Thickness mm 0.04 0.04 Density g/cm³ 0.25 0.25 Sucking height mm 13 8Liquid retention μm 1.6 0.6 h²η/γt

As is seen in the above Table 1, liquid retention is improved whenseparator is coated in accordance with this invention.

As explained above, a separator which has been coated in accordance withthis invention improves in electrolyte retention. When used inelectrical and electronic parts, a coated separator of this invention isexpected to help said parts to show their original electrical propertieswithout such loss as caused by the insufficient retention or leak ofelectrolyte.

1. A separator for electrical and electronic parts which is coated withat least one substance selected from ionic substances, hydroxylgroup-containing substances and silicon compounds.
 2. A separator ofclaim 1 wherein said ionic substances are selected from calciumcarbonate, calcium chloride, anhydrous calcium chloride, calcium oxide,sodium chloride, sodium sulfate, anhydrous sodium sulfate, sodiumsulfite, copper sulfate, anhydrous copper sulfate, aluminum sulfate andsodium carboxymethylcellulose.
 3. A separator of claim 1 wherein saidhydroxyl group-containing substances are selected from alcohols, glycolsand polysaccharides.
 4. A separator of claim 1 wherein said siliconcompounds are selected from silica gel, silica sol, silica and zeolite.5. A separator of claim 1 which is selected from paper, non-wovenfabric, fine porous film and a composite thereof.
 6. A separator ofclaim 1 which is made from a material selected from aramid, polyester,polypropylene, polyethylene, polyphenylene sulfide, fluoroplastic,polyvinyl alcohol, PBO (poly-para-phenylene benzobisoxazole), polyimide,glass, carbon, alumina, natural fiber and natural pulp.
 7. A separatorof claim 1 which is subjected to heat treatment before and/or aftercoated.
 8. A separator of claim 1 which has a sucking height in a rangeas shown by the following inequality (2):0.7<h ² η/γt   (2) wherein h denotes the height (mm) to which a liquidis sucked up within a period of t seconds; η denotes the viscosity (mP aS) of said liquid; γ denotes the surface tension (mN/m) of said liquid;and t denotes sucking time (second).
 9. A process to manufacture aseparator of claim 1 which is characterized by the following steps: atleast one substance selected from ionic substances, hydroxylgroup-containing substances and silicon compounds is previouslydissolved or dispersed in water; subsequently, an uncoated separator issoaked in the resultant solution or dispersion; and then, said separatoris dried so that moisture may be evaporated.
 10. A process of claim 9which is characterized by the following steps: an uncoated separator ispreviously integrated with a part before soaked in a solution;subsequently, thus assembled whole part is soaked in a solution; andthen said whole part is dried so that moisture may be evaporated. 11.Electrical and electronic parts wherein a separator of claim 1 is used.